If the mag24 is on the same floor as the tank, you'll be cleaning up the mess when the tank overflows. I doubt any overflow sized for a 90g tank would keep up with that much flow. Without knowing what skimmer your using, a rough estimate of around 6x turnover rate would be about 500-550gph at the return is what you should aim for, and run the powerheads. Now, if you want to use the mag24 as a closed loop pump, that would be a good size pump to run four 1/2" closed loop returns thru out the tank.